As a component to control a large current of an electric vehicle and a train, a power semiconductor module is used. A thermoelectric module is used in an apparatus to perform a power generation with a waste heat, a thermostatic apparatus in a semiconductor process, and an apparatus to cool an electronic device. In these electronic component modules, as a substrate to mount a power semiconductor element or a thermoelectric element, a circuit board in which metal plates are bonded to both surfaces of a ceramic substrate is used (refer to Patent References 1 and 2).
For example, electronic components of the power semiconductor element and the thermoelectric element are soldered on one metal plate of the circuit board, the other metal plate is soldered on a base plate including a metal plate and a composite substrate to be fixed. A structure have been also known, in which a thin semiconductor element is sandwiched between electrode blocks good in an electric conductivity such as copper, and the surroundings are constituted in an airtight seal structure and pressurized from outside of the electrode blocks to integrate plural electronic components (refer to Patent Reference 3).
In the case that electronic components composing the power semiconductor module and the thermoelectric module are Si elements and thermoelectric elements for temperature adjustment, the maximum operating temperature of these is about 125° C., even though, they are fixed by means of soldering with a conventional lead solder and a pressure contact, they can sufficiently endure a uniform heating and a heat cycle (for example, a room temperature to 125° C.).
However, regarding power semiconductor modules and thermoelectric modules in the future, there is a problem, as follows. For example, in the case of using a wide gap semiconductor single crystal element of a high temperature operation type such as SiC element instead of the Si element, they are required to operate under the high temperature environment such as at 300 to 500° C. to exhibit the characteristic sufficiently. In the case when the SiC element operating under the high temperature environment is fixed on a circuit board by conventional soldering, the operation temperature of the SiC element leads the fixing state to the circuit board to be unstable, which causes peeling of the SiC element.
In the case of using a thermoelectric module operable under the high temperature environment, electric energy can be created from a high temperature waste heat of about 500° C. emitted from, for example, a vehicle and a factory, so that reduction of an environmental burden is expected. However, similar to the power semiconductor module, in the case when the thermoelectric element used under the high temperature environment is fixed on a circuit board by conventional soldering, the fixing state of the thermoelectric element to the circuit board can not be maintained stably. In the thermoelectric module, in order to prevent diffusion and release stress, a titanium layer as an intermediate layer is interposed between the thermoelectric element and the electrode (refer to Patent Reference 4). Herein since the intermediate layer and the electrode are formed by thermal spraying method, there is a difficulty in a manufacturability of the thermoelectric module.
In order to improve a fixability of electronic components under the above-described high temperature environment, it is understandable to bond the electronic components such as the SiC element and the thermoelectric element to the circuit board by a high temperature solder. However, in recent years, it is desired to be lead-free of solder, and even in the case of soldering electronic components onto a circuit board, it is desired to use solder not including lead. Since the high temperature solder not including lead has a difficulty in obtaining a characteristic more equivalent to the conventional one, it is practically difficult to bond the electronic components such as the SiC element and the thermoelectric element to the circuit board by the high temperature solder.
Further, in terms of a yield and a reliability, the element size of the semiconductor element and the thermoelectric element is miniaturized, and it is expected that the number of the elements mounted is to be increased significantly by miniaturization of the element size. Therefore, in the power semiconductor module, it is expected that the operating temperature is to be higher and higher. As the operating temperature of the power semiconductor module becomes higher, the heat cycle becomes larger, and an oscillation caused by a thermal deformation and a thermal expansion difference is increased. Accordingly, it makes it easier that the electronic components such as the SiC element are peeled from the circuit board, and it becomes further difficult to secure a reliability.
Patent Reference 1: JP-A 2002-201072 (KOKAI)
Patent Reference 2: JP-A 2002-203993 (KOKAI)
Patent Reference 3: JP-A Hei 10-098140 (KOKAI)
Patent Reference 4: JP-A 2003-309294 (KOKAI)